Fly to Buffalo, rent a car, then drive to Toronto.
I did the same thing before I got my US GC last year. Easy. The Canadian border officer asked me how long I had stayed in US and why I went to US. I said I was a consultant and had a project in US, and I stayed in US for 1 month for the project (actually I stayed in US for more than 2 yrs after getting maple card, haha). Then he asked : "any wine? drug?...".
Then he asked:"how could you go to US". I replied: "I have H1B visa". Then he sounded satisfied: "oh, H1B, good, welcome back!". Then I thanked him and drove to Toronto to enjoy the good Chinese food. : )